docs: def _set_metadata(element, metadata, attr_map, transform=str):
      """
      Set metadata attributes on a given ``element``.
  
      :param element:
          :class:`xml.etree.ElementTree.Element` instance
      :param metadata:
          Dictionary of metadata items containing attribute data for ``element``.
      :param attr_map:
          Dictionary mapping of metadata key->attribute name.
      :param transform:
          A function accepting and returning a single value to be applied to each
          attribute value. Defaults to `str`.
      """
      for kw, attr in attr_map.items():
          value = metadata.get(kw)
          if value is not None:
              element.set(attr, transform(value))